1. Field of the Invention
The present invention relates to a tube unit of a spark plug for an engine. More particularly, the present invention relates to a tube unit of a spark plug for an engine that is mounted in a cylinder head so as to mount a spark plug in the cylinder head.
2. Description of Related Art
Generally, natural gas engines or gasoline engines have an ignition device for igniting an air-fuel mixture supplied to a combustion chamber, and such an ignition device includes a spark plug that is fed high voltage from an ignition coil and generates a spark in a cylinder of an engine.
As shown in FIG. 5, a spark plug 101 is mounted at an upper portion of each cylinder head 103 in an engine by a spark plug tube 107 provided with an o-ring 105.
The spark plug tube 107 is provided with an interior mounting hole 109 for mounting the spark plug 101, and an ignition coil tube 111 is mounted at an upper portion of the cylinder head 103 by a tap 113 so as to connect the spark plug 101 to an ignition coil.
In this case, a lower portion of the spark plug tube 107 is threaded to a penetration hole 117 of a lower deck 115 that corresponds to a combustion chamber of the cylinder head 103.
For preventing the spark plug tube 107 from being coming out of the penetration hole 117 and coolant from leaking to the combustion chamber, an adhesive such as Loctite® is applied to an exterior circumference of the lower portion of the spark plug tube 107.
According to a conventional spark plug tube, the Loctite is degraded by heat and pressure created at the combustion chamber and coolant leaks into the combustion chamber. Therefore, the engine is damaged.
Since the spark plug tube expands by heat, screw thread of the spark plug tube may be broken in a case of installing or removing the spark plug, and it may come out of the penetration hole of the lower deck in a case of repairing the spark plug.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.